Energy
Momentum, Collisions,
Impulse
Momentum
A
measure of how
hard it is to stop a
moving object
 Momentum
=
(MASS)
(VELOCITY)
Momentum
Equation
p= m v
Units
p= mv =
(kg)(meter) =
second
kg·m
s
Momentum animations

http://physics.weber.edu/amiri/director/Mo
mentum.html
Momentum Example 1
What is the momentum of an orange
with a mass of 0.5kg
thrown with a velocity of 5.0 m/s?
m = 0.5kg
v = 5.0 m/s
p = mv = (0.5kg)(5.0 m/s) =
2.5 kg·m
s
Momentum Example 2
An object with a mass of 3.0 kg is traveling
at a velocity of 4.0 m/s .
What is its momentum?
More momentum examples

http://id.mind.net/~zona/mstm/physics/m
echanics/momentum/introductoryProblem
s/momentumSummary1.html
Conservation of Momentum
Newton’s Third Law
For every action there is an equal
and opposite reaction!
 To accelerate an object, we must
apply force
Conservation of Momentum
 Force(s)
must be external
 Internal forces do not apply
E.g. to accelerate a car,
do you push
on the dashboard?
Conservation of Momentum

http://id.mind.net/~zona/mstm/physics/m
echanics/momentum/introductoryProblem
s/momentumSummary3.html
Collisions
Net momentum before collision =
Net momentum after the collision
Elastic Collisions

http://id.mind.net/~zona/mstm/physics/m
echanics/momentum/solvers/momentumS
olvers1.htm
Inelastic Collisions

http://id.mind.net/~zona/mstm/physics/m
echanics/momentum/solvers/momentumS
olvers1.htm
Impulse
= force exerted over time
Impulse changes momentum
Impulse
Equation
J = (Force) (time)
J = Ft
= mΔv = Δp =
m (v2-v1) = Δp
(mass)(change in velocity) =
change in momentum
Impulse
Units
J= (Newton) (seconds)
J = N·s
 Force is in Newtons
 Time is in seconds
Impulse Example
An 8N force acts on a 5 kg object
for 3 seconds. If the initial
velocity of the object was 25 m/s,
what is its final velocity?
F= 8 N m= 5 kg
t= 3 s
v1 = 25 m/s
v2 = ?
J = Ft =(8N)(3s) = 24 N·s
BUT we need to find v2 ………
Impulse Example
J = mΔv = m (v2-v1) =
24 N·s = 5 kg(v2 - 25 m/s) =
24 = 5 v2 - 125 m/s =
125+24= 5 v2 = 149/5 = v2 =
29.8 m/s
Impulse problems

http://id.mind.net/~zona/mstm/physics/m
echanics/momentum/introductoryProblem
s/momentumSummary2.html